How many particles have momentum in a specific interval?

[najima]

Homework Statement

a pulse 1 m long contains 1000 α particles.at t=0,each α particles in the state

ψ(x,0){1/10e^(-ik_0 ) lxl≤50cm,k_0=π/50 and 0 for elsewhere,}
at t=0 ,how many particle s have momentume in the interval 0<hk<hk_0?

Homework Equations

introduction to quantum mechanics by liboff chapter 5/problems 4

The Attempt at a Solution

I don't understand what does it mean! I think I have to calculate expectation value?am I right?

 

[HallsofIvy]

Expectation value of what? You are asked for the number of particles within a certain range of momenta. Since you know there are 1000 particles it would be sufficient to determine the percentage within that range. Looks to me like you want to calculate the probabilty a given particle has that momentum.

 

[najima]

I can't get the answer ,please, help more.:-(

 

[najima]

oh !finally I got! thax man!